Caption: Wave equation. This equation describes the behaviour of waves such as sound waves, light waves and water waves. x represents a spatial variable, t is time, u is a scalar function, c is a fixed constant, the italic 'd' symbol is the partial derivative. The wave equation for a single dimension was formulated in 1746 by French mathematician Jean-Baptiste le Rond d'Alembert who was studying violin strings. The Swiss scientist Leonhard Euler in 1707 discovered the wave equation in a three space dimension.